This invention relates generally to RF amplifiers, and more particularly to RF gridded traveling wave tubes (GTWT's).
A GTWT is basically a wide band, high power RF amplifier which is grid controlled to allow for highly flexible usage in transmitters requiring numerous modes of operation at different pulse repetition frequencies (PRF's) and pulse widths. As such, GTWT's are often used in high power radar transmitters. One problem which has been found to exist, however, in such radar usage has been meeting the requirement of continuously operating the GTWT at saturation to provide optimum radar performance. Such operation is desirable inasmuch as RF power output is maximized and the RF noise is minimized when the GTWT is at saturation.
The prior art approach to resolving this problem has basically revolved around providing an equalizer (a passive filter device) installed at the tube manufacturer in the input of the GTWT. This device attenuates the drive to the GTWT at certain points in a perdetermined frequency band such that it will always be saturated or close to saturation. However, in order for the equalizer to operate properly, the radar master oscillator (RMO) and the transmitter power supplies must be set to tight tolerances to provide an RF drive within the narrow ranges the equalizer can control (e.g. 50 mw .+-. 1db in a typical high power radar). Also, any drift due to aging or temperature of the RMO or the power supplies in the transmitter may cause either unit to be out of tolerance. When the RF is not optimized, the RF output power drops, the AM noise on the RF output power increases, and the shape of the RF output power pulse changes which may cause the RF spectrum shape to be out of tolerance.